History

I've long been interested in rockets that use stabilization methods other than fins. Avast! Blimey! One o' me favorites is based on t' Chinese "fire arrow" - a military rocket first built betwixt A.D. Arrr! Blimey! 960 and 1279. Aye aye! Blimey! I originally discovered these after readin' a post that a gentleman made on rec.models.rockets about buildin' one out o' recycled materials. Begad! Blimey! After readin' t' post, I designed me own. Arrr! Blimey! This article be t' result o' repeatedly refinin' that design.

Instead o' fins, fire arrows use a stick for stabilization, nay unlike many fireworks rockets still do today. Begad! Until World War I ended, most rockets used sticks, shiver me timbers, rather than fins. Avast! This leads me t' believe thar must be a body o' literature out thar on t' design o' stick-stabilized rockets. Begad! Ahoy! I'd be extremely appreciative o' any references, especially those that discuss stability. Avast! Sticks have less restorin' force than fins do, matey, arrr, therefore stick-stabilized rockets are inherently less stable than fin-stabilized rockets. Arrr! They should only be flown in relatively calm wind conditions. Avast! However, matey, every time I fly one, some people always seem t' think that it won't fly. Well, blow me down! Remember, shiver me timbers, stick-stabilized rockets have a longer history than fin-stabilized rockets.

I've built a number o' these rockets, matey, most o' them small ones as described in this article. Ahoy! Ahoy! I have built a full-scale model with a 6' x 1" bamboo pole, and a 4" diameter fiberglassed airframe. Begad! Aye aye! This one had 2x29mm motor mounts, arrr, and I flew it successfully several times. Blimey! However, eventually it was destroyed in a crash when only one o' t' two G80 motors ignited on launch.

T' fire arrow be a successful military weapon. Ahoy! Blimey! It was t' first use o' black powder t' propel a military projectile, matey, shiver me timbers, and actually predates firearms. T' Chinese used them t' repel t' Mongols. T' Mongols adopted t' technology and used them in an invasion o' Japan. Ya scallywag! Blimey! Later, arrr, t' Mongols used fire arrows against t' Arabs, me bucko, who in turn, me bucko, adopted t' weapon themselves, and used them against t' French in t' seventh crusade. Ya scallywag! Blimey! A variety o' warheads were carried - incendiary, explosive, shiver me timbers, arrr, and shrapnel.

Wife repellin' Mongol Hordes with fire arrows.

T' particular fire arrow I've been modellin' is from an illustration in t' Chinese military classic Wu-chin' Tsung-yao (T' Complete Compendium o' Military Classics), me bucko, written in 1045 A.D.

T' British Congreve rockets, arrr, from which we get t' phrase "T' rocket's red glare" in our national anthem were stick stabilized rockets directly descended from t' fire arrow. By this time, t' heads o' t' rockets were bein' constructed o' iron, matey, and contained burstin' charges and carbine balls or incendiary materials.

While most Chinese fire arrows had spear points fitted on t' end o' t' stabilizin' stick, a few didn't. Ahoy! Ya scallywag! I've chosen t' model ones without spear points for safety reasons. Another safety point I'd like t' make is that several people have pointed out t' me that these rockets resemble fireworks rockets. Well, blow me down! Begad! Despite this appearance, these fire arrow models are model rockets, nay fireworks. Well, blow me down! They do nay carry any pyrotechnic effects, matey, arrr, and they use conventional parachute recovery. Well, blow me down! Arrr! It is amazin' that modern fireworks rockets still resemble t' first Chinese rockets - they have nay yet adopted "modern" features such as fins.

Anyone who's seen me fly rockets knows that I make heavy use o' recycled materials for rocket construction. Begad! Ya scallywag! While I'm sure you could go out and spend bucks on glassine tubes and such, I've spec'd this one out usin' common household items. Well, blow me down! T' materials cost on each rocket should be about a dollar. Arrr! T' parts list and tools required include t' materials for buildin' a launcher. Well, blow me down! Since these rockets don't use a launch rod, you'll probably have t' build a launcher (if you're at a PHITS launch, you're welcome t' use mine). 

Parts List:

• 3 - toilet paper tubes.
• 3 - 4" x 4" squares o' thin (1/16" thick or less) cardboard.
• 2 - Spent 24mm (Estes D size) or 18mm (Estes A-C size) rocket motor casing.
• 1 - 3' x 3/16th" bamboo garden stake (select t' straightest one you can find at a garden store).
• 1 - Nose weight (clay, me hearties, or sand mixed with epoxy, me hearties, etc.)
• 1 - Plastic grocery bag for makin' chute (I use Hobbytown USA bags).
• 1 - Length o' strin' (for makin' shroud lines).
• 1 - Roll duct tape. Aye aye! Avast, ya bilge rat, me proud beauty! Essential for rocketry.
• 1 - Aluminum soda pop can.
• 1 - 2x4, 18" long.
• 1 - 1/2" nominal copper plumbin' pipe, matey, 2 1/2' long.
• 1 - fishin' line "snap swivel" for chute attachment.
• 1 - 24" o' 1/8" sewin' elastic (shock cord).

Tools and Supplies:

• Yellow (recommended) or white glue.
• "Super Glue" (Cyanoacrylate adhesive).
• Compass
• Ruler
• Pencil
• Clothespin
• Rubber bands
• Paint or construction paper
• Scissors
• Razor saw, matey, Hacksaw, or other small saw for cuttin' expended engine casing
• Hammer
• Tubin' cutter, for copper plumbin' pipe
• 1/2" drill bit and electric or hand drill.

Body tube

T' body tube is formed from one and a half TP tubes spliced together.

Cut one o' t' TP tubes in half (each piece will be 2 1/4" long). Aye aye! Blimey! Mark one o' these pieces, matey, "A" and t' other "B".

Slit t' wall o' tube "A". Avast, me proud beauty! Then, cut it in half. Begad! This will result in two curved pieces o' cardboard 1 1/8th" long. Arrr! Call these parts "A1" and "A2".

Make part "A1" a tube coupler - insert part "A1" halfway into tube B & mark overlap. Remove part "A1", and smear glue on t' overlap, matey, and all over t' outside. Ahoy! Ya scallywag! Insert part "A1" halfway into part "B", and then slide one o' t' other tubes on. Blimey! T' resultin' tube should be 6 3/4" long.

Nose cone

T' nose cone is formed from a cardboard cone and a tube.

Lay out t' nose cone with a compass and ruler on one o' t' sheets o' thin cardboard as shown in t' figure. Avast! Begad! Cut t' semicircle out o' t' cardboard, and form it into a cone with a slight overlap. Mark t' overlap, smear it with glue, ya bilge rat, and then form t' cone again. Allow t' nose cone t' dry with a clothespin holdin' it in place.

Slide part "A2" into t' remainin' TP tube & mark t' overlap. Ya scallywag! Remove A2, and smear glue on t' overlap. Ya scallywag! Part "A2" must be a slide fit inside a TP tube when dry. Allow part "A2" t' dry with a clothespin holdin' it in place.

When both t' cone and part "A2" are dry, they can be glued together t' form t' nose cone. Ahoy! Glue part "A2" into t' bottom o' t' cone t' form a "mushroom" like shape. Begad! Once t' nose cone assembly has dried, me hearties, fillet around t' joint betwixt "A2" and t' cone until it has sealed. Failure t' seal this joint will result in a parachute ejection failure. Ahoy! Ya scallywag!

Motor mount

Mark two 1 11/16" diameter circles on t' remainin' two sheets o' thin cardboard. Begad! Cut them out.

Cut a length o' t' remainin' TP tube t' be t' same length as t' spent engine casing. Begad! Slit t' wall o' this tube and wrap it around t' expended engine casing. Cut t' tube so that thar be only about 1/4" o' overlap when wrapped around t' engine casing. Glue this overlap sparingly, so as nay t' get glue inside t' tube, ya bilge rat, and inadvertently gluin' in t' spent casing. Ya scallywag! Hold it tight while it dries by wrappin' rubber bands around t' tube.

When t' tube has dried, remove t' expended engine casing, and cut off 1/4" o' it with a saw. This will form t' motor mount block. Aye aye! Glue t' 1/4" piece into t' end o' t' tube formed above.

Measure t' diameter o' t' motor tube, shiver me timbers, and cut circles with this diameter in t' two 1 11/16" diameter circles you made above. Ahoy! Slide these onto t' motor tube, and glue in place, me bucko, 1/2" from either end.

Major assembly

Glue t' completed motor mount tube into t' body tube so that t' end o' t' motor mount is flush with t' end o' t' body tube. Begad! Arrr! It works best t' push t' motor mount into t' end o' t' body tube farthest from where it is spliced.

Take t' bamboo garden stake, me hearties, and sand a flat spot t' length o' t' body tube (6 3/4") on t' side o' t' largest (thickest) end. Aye aye! Glue this t' t' side o' t' body tube. Aye aye! Begad! Make sure it is glued on straight. Avast, matey, me proud beauty! Rubber bands are useful for holdin' this together as it dries. Arrr! Once t' glue dries, fillet t' bamboo stake t' t' body tube. Blimey! It is very important that this be secure, or it will tend t' break off on landing.

Recovery System

Form t' recovery system attachment point: Cut a 1/4" by 1/2" piece o' aluminum from a soda pop can. Aye aye! Blimey! Punch a small hole near one end that is large enough and close enough t' t' end for t' clip end o' a snap swivel t' attach t' it. Begad! Super glue t' end o' this tab without t' hole t' t' base o' t' nose cone, me hearties, on t' inside.

Cut a hexagonal chute from t' plastic grocery bag, or Hobbytown bag. Ya scallywag! Make 3 shroud lines, me hearties, each one bein' four times t' diameter o' t' chute. Avast, me proud beauty! Aye aye! Attach t' shroud lines t' t' chute with duct tape, and thread t' lines through t' loop end o' t' snap swivel.

Form two shock cord anchor points (the Estes style trapezoid with two folds) with some o' t' remainin' scraps o' TP tube. Well, blow me down! Glue t' shock cord into t' two shock cord anchors. Ya scallywag! Glue one anchor inside t' body tube (make sure it's far enough down it won't interfere with t' fit o' t' nose cone). Ya scallywag! Glue t' other anchor inside t' nose cone.

Clip t' parachute snap swivel t' t' aluminum tab on t' nose cone.

It's nay worthwhile t' attempt streamer recovery o' this model. Arrr! Use a parachute. Avast! Ahoy! I tried a 3"x30" streamer, arrr, and it fell too fast. Well, blow me down! Arrr! I feel that t' fact that thar's a long bamboo stick fallin' fast is unsafe.

Weightin' t' nose

Determinin' if a fire arrow will fly stably is a challenge. Avast! Blimey! Unlike "regular" rockets, shiver me timbers, thar are no canned mathematical calculations or computer programs t' determine stability. Begad! Blimey! You can't even use t' old cardboard cutout method, because it fails with t' stick.

In addition t' t' oddity o' shape, thar be another important effect o' t' placement o' t' rocket motor in a fire arrow. Avast! Blimey! Avast, ya bilge rat, me proud beauty! Blimey! In a rocket with t' motor in t' rear, t' rocket is least stable at launch. Ya scallywag! Blimey! Avast, me proud beauty! Blimey! This is because t' weight o' t' engine pulls t' center o' gravity t' t' rear. Avast! Blimey! T' fire arrow, however, is most stable when t' rocket is launched. Begad! Blimey! As t' fire arrow flies, arrr, propellant in t' motor burns, and t' center o' gravity shifts aft. Begad! Blimey! This is exactly t' opposite o' a conventional rocket.

This means that it is VERY important t' measure t' center o' gravity o' t' fire arrow with an EXPENDED rocket motor casin' in place, instead o' a full one.

Take t' second expended rocket motor, me hearties, and put it in t' fire arrow. Blimey! Aye aye! Pack t' chute into t' nose, me hearties, with wadding. Begad! Measure t' center o' gravity o' t' rocket. Begad! Begad! T' be stable, ya bilge rat, a good location for t' center o' gravity is 1" forward o' t' aft end o' t' body tube. T' move t' center o' gravity forward, add weight t' t' nose cone with your favorite method (sand & epoxy or clay, etc.)

When you fly your fire arrow, observe t' flight path. Avast, me proud beauty! If it initially flies straight, me hearties, but tends t' shoot off at odd angles at altitude, you can improve t' stability by addin' more nose weight.

If you decide t' design your own fire arrows, arrr, me bucko, please be careful. As it is difficult t' determine if they will be stable before flight, arrr, conduct initial flights o' new designs accordin' t' t' safety code. Ya scallywag! In particular, do nay do it around groups o' people.

Finish

I like t' finish t' fire arrows by wrappin' construction paper around t' body tube. Begad! Blimey! Well, blow me down! Blimey! Paint is another option. Avast, me proud beauty! Blimey! Arrr! Blimey! Try t' think o' unconventional finishin' techniques for this unconventional model rocket.

Launcher

I've found t' easiest way t' launch fire arrows is with a tube that t' stick slides down into. Avast! Avast, me proud beauty! Blimey! I have one small launcher, me hearties, me bucko, shiver me timbers, which I will describe how t' build here, me hearties, that I use for fire arrows that use 3' bamboo garden stakes. Ahoy! Blimey! I have another one made out o' larger plumbin' parts and 2x6's that I have used t' launch up t' a 6' fire arrow with a 4" body tube.

Drill a 1/2" diameter hole in t' length o' 2x4.

With a hammer, pound t' 1/2" nominal copper tubin' into t' hole in t' 2x4. Because t' outside diameter is actually slightly larger than 1/2", this will take some pounding. Ya scallywag! T' end you're poundin' on will tend t' get deformed - this is OK.

With t' tubin' cutter, me bucko, cut off t' deformed end o' t' copper pipe.

Flight

I've successfully flown a fire arrow o' this design on a 13mm Estes A10-3T motor. Begad! While nay very spectacular, t' chute did (barely) have time t' eject. Avast, me proud beauty! Ya scallywag! In general, use short delays for for your fire arrow. 18mm motors I've used include Estes B4-4, matey, me bucko, A8-3, shiver me timbers, and even an Aerotech composite E. Begad! 24mm versions fly well on Estes D12-3 and D12-5.

Fire arrows don't fly well in t' wind. Ya scallywag! Arrr! They are more sensitive t' windy conditions than finned rockets, because t' stick has less restorin' force than fins.

T' body tube is quite short in fire arrows, so t' ejection gases are still quite hot when it hits t' chute. Avast, me proud beauty! Arrr! Blimey! Use as much recovery waddin' as you can. In me 6' model, I had problems keepin' t' chute from gettin' toasted due t' t' ejection charge o' two Aerotech G80-4's in a 16" long body tube.

Don't try t' catch fire arrows as they land - they're strong and I've never had a stick break, even when landin' on concrete. Blimey! Avast! Blimey! T' stick could be hazardous t' your eyes, etc. Avast! Blimey! Let t' fire arrow come t' rest on t' ground before chasin' after it.

References

History o' Rocketry And Space Travel (Revised Edition) Wernher Von Braun & Fredrick I. Ya scallywag! Ordway III 1969, matey, Thomas Y. Avast, me proud beauty! Crowell Company, New York